This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-012119, filed Jan. 19, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetic recording medium comprising a magnetic film suitable for use in high-density magnetic recording.
2. Description of the Related Art
In conformity with the recent trend to enhance the processing speed of computer, it is now demanded to enhance the speed and density of magnetic storage apparatus (HDD) that is designed to perform recording and reproducing of information. As the isolation and fineness of magnetic particles have been enhanced in the multigrain magnetic recording medium in responding to such a demand as described above, a problem is now raised in recent years with regard to deterioration of recorded magnetization due to thermal fluctuation. As a criterion for the thermal fluctuation resistance of magnetic recording medium, KuV/kT (where Ku, V, k and T represent magnetic anisotropic energy density, activation volume in relation to magnetization reversal, Boltzmann constant, and absolute temperature, respectively) is generally employed. If the value of KuV/kT is 80 or more, the magnetic recording medium is considered as being thermally stable. Assuming that the particle diameter of magnetic fine particle is made about 3 nm and thickness of the recording layer is made about 10 nm with the trend to enhance the density, a high Ku value of not less than 107 erg/cc is required. As for the magnetic materials exhibiting a high Ku value at room temperature, ordered phase alloy such as FePt, FePd, and CoPt are known. Use of these materials for a magnetic layer makes it possible to enhance thermal fluctuation resistance considerably. These materials exhibit very high Ku in the c-axis direction only when they form a crystal structure called L10 (CuAu-I type) structure in which a face-centered tetragonal lattice (fct) is constructed such that the {001} plane is occupied by a magnetic element, and the {002} plane is occupied by a noble metal element (alternatively, the {002} plane is occupied by a magnetic element, and the {001} plane is occupied by a noble metal element). However, it is impossible to form an ordered phase exhibiting the aforementioned crystal structure only by a deposition method commonly employed in the manufacturing process of HDD medium such as sputtering and electron-beam evaporation. It is required, for forming substantially perfect ordered phase, to perform deposition under the condition where the substrate is heated to 500xc2x0 C. or more, or to perform annealing at 500xc2x0 C. or more after deposition of the film. However, such a high-temperature process is unsuitable to a usual deposition apparatus employed in a conventional manufacturing process of the HDD medium. Therefore, in order to put a magnetic recording medium employing an ordered phase alloy-based material into practical use, it is required for lowering the substrate temperature or annealing temperature.
As described above, although the ordered phase alloy is considered promising as a material for enhancing the thermal fluctuation resistance, the substrate temperature or annealing temperature required for forming the ordered phase should be lowered to put the ordered phase alloy into practical use.
Therefore, an object of the present invention is to provide a magnetic recording medium capable of lowering a substrate temperature or an annealing temperature required for forming the ordered phase.
A magnetic recording medium according to an aspect of the present invention comprises: a substrate; an underlayer formed on the substrate; a magnetic layer formed on the underlayer, wherein the magnetic layer comprising crystal grains having (a) an L10 structure mainly including Fe and Pt, and (b) 0.1 to 50 atomic percent of at least one element selected from the group consisting of Cu, Au, Zn, Sn, Pd and Mn; and a protective layer formed on the magnetic layer.
A magnetic recording medium according to another aspect of the present invention comprises: a substrate; an underlayer formed on the substrate; a magnetic layer formed on the underlayer, wherein the magnetic layer comprising crystal grains having (a) an L10 structure mainly including Fe and Pd, and (b) 0.1 to 50 atomic percent of at least one element selected from the group consisting of Cu, Au, Zn, Sn and Mn; and a protective layer formed on the magnetic layer.
A magnetic recording medium according to still another aspect of the present invention comprises: a substrate; an underlayer formed on the substrate; a magnetic layer formed on the underlayer, wherein the magnetic layer comprising crystal grains having (a) an L10 structure mainly including Co and Pt, and (b) 0.1 to 50 atomic percent of at least one element selected from the group consisting of Ni, Au and Mn; and a protective layer formed on the magnetic layer.